The present invention refers to a clamping apparatus, comprising a first coupling element provided with at least three centering pins having at least partially conical shape and a second coupling element adapted to be releasably attached to said first coupling element. The second coupling element is provided with a number of grooves corresponding to the number of the centering pins provided on the first coupling element such that the centering pins provided on the first coupling element engage the grooves when the second coupling element is attached to the first coupling element.
The first and second coupling elements both are provided with Z reference stop surfaces adapted to cooperate such as to determine the position of the second coupling element with regard to the first coupling element in Z-direction when the second coupling element is attached to the first coupling element.
Such clamping apparatuses are preferably used for clamping a coupling element provided with a workpiece or with several work-pieces in a well-defined position in the machining area of a machine tool. The one coupling element provided with the workpiece is usually designated as workpiece carrier or pallet, while the other coupling element, fixed in the machining area of the machine tool, is usually designated as chuck.
In known clamping apparatuses, one of the coupling elements, i.e. the chuck, is provided with four centering pins, each comprising two conical lateral surfaces. The other coupling element, i.e. the workpiece carrier or pallet, is provided with four grooves, corresponding to the four-centering pins as far as position and shape is concerned. During the operation of clamping the workpiece carrier to the chuck, the centering pins engage the grooves and align the workpiece carrier with regard to the chuck in X- and Y-directions as well as with regard to its angular position around the Z-axis. A fundamental disadvantage of such known clamping apparatuses may be seen in the fact that the centering pins may jam or seize in the grooves upon clamping the workpiece carrier to the chuck.